Well, sure. In the landlord's case, interest is a business expense that's netted out against rental business income . The landlord can't deducted it from his personal income taxes, the way an owner-occupied resident.
It’s a deduction no matter how you slice it. Personally, I’d do away with deductions & go to a flat rate period. My tax sheet would consist of 1 page. It would be very simple. All income under $100,000 is taxed at 10%, all income over 100k is taxed at maybe 15%. Shrink government till it can manage with that amount of revenue.